使用renderInContext：用于由cgpaths创建的掩码

Question

I recently found out that the renderinContext: method ignores any layer masks. I am trying to capture a video of my app's screen, in which I animate the path of a masked CALayer.

To record the screen, I am using the ScreenCaptureView class, found online. The view takes a "screenshot" of it's subviews every x seconds and compiles them into a video.

In the drawRect method, I call

[[self.layer presentationLayer] renderInContext:context];

After looking online, I found someone's solution; however, it applies for masks that are images. (My mask is a CGPath).

-(UIImage*) imageFromView:(UIView*)originalView
{
    //Creating a fakeView which is initialized as our original view.
    //Actually i render images on a fakeView and take screenshot of this fakeView.
    UIView *fakeView = [[UIView alloc] initWithFrame:originalView.frame];

   [fakeView.layer setMasksToBounds:originalView.layer.masksToBounds];

            //Getting subviews of originalView.
            for (UIView *view in originalView.subviews)
            {
                //Getting screenshot of layer of view.
                UIGraphicsBeginImageContext(view.bounds.size);
                [view.layer renderInContext:UIGraphicsGetCurrentContext()];
                UIImage *imageLayer = UIGraphicsGetImageFromCurrentImageContext();
                UIGraphicsEndImageContext();

                //If it is masked view, then get masked image.
                if (view.layer.mask)
                {
                    //getting screenshot of masked layer.
                    UIGraphicsBeginImageContext(view.bounds.size);
                    [view.layer.mask renderInContext:UIGraphicsGetCurrentContext()];

                    //PNG Representation is most important. otherwise this masked image will not work.
                    UIImage *maskedLayerImage=[UIImage imageWithData:UIImagePNGRepresentation(UIGraphicsGetImageFromCurrentImageContext())];
                    UIGraphicsEndImageContext();

                    //getting image by masking original image.
                    imageLayer = [self maskImage:imageLayer withMask:maskedLayerImage];
                }

                //If imageLayer is pointing to a valid object, then setting this image to UIImageView, our UIImageView frame having exactly as view.frame.
                if (imageLayer)
                {
                    UIImageView *imageView = [[UIImageView alloc] initWithFrame:view.frame];
                    [imageView setImage:imageLayer];
                    [fakeView addSubview:imageView];
                }
            }

            //At the end, taking screenshot of fakeView. This will get your Original Image.
            UIGraphicsBeginImageContext(fakeView.bounds.size);
            [fakeView.layer renderInContext:UIGraphicsGetCurrentContext()];
            UIImage *previewCapturedImage = UIGraphicsGetImageFromCurrentImageContext();
            UIGraphicsEndImageContext();
            return previewCapturedImage;
        }
}

//Method is used to get masked image.
- (UIImage*) maskImage:(UIImage *)image withMask:(UIImage *)maskImage
{
    CGImageRef maskRef = maskImage.CGImage; 
    CGImageRef mask = CGImageMaskCreate(CGImageGetWidth(maskRef),
                                        CGImageGetHeight(maskRef),
                                        CGImageGetBitsPerComponent(maskRef),
                                        CGImageGetBitsPerPixel(maskRef),
                                        CGImageGetBytesPerRow(maskRef),
                                        CGImageGetDataProvider(maskRef), NULL, false);

    CGImageRef masked = CGImageCreateWithMask([image CGImage], mask);

    return [UIImage imageWithCGImage:masked];
}

Can I do something similar for masks from cgpaths?

Answer 1

You can use CGContextClip() in renderInContext: to clip to a path:

- (void)renderInContext:(CGContextRef)context {

    // Assign maskPath to whatever path you want to mask to (Here, it's assumed that your layer's mask is a CAShapeLayer)
    CGPathPathRef maskPath = [(CAShapeLayer *)self.mask path];
    CGContextAddPath(context, maskPath);
    CGContextClip(context);

    // Do drawing code here
}